01604 212732
7:30am - 10pm
Head Office: 3 Sunningdale Close, Northampton NN2 7LR
THS Plumbing & Heating Northampton
our gas safe id: 517522

Most common Vaillant boiler faults

The F75 fault is typically the most popular vaillant failure and the fault is either the water pressure sensor or faulty pump. If you have this fault, you’ll need a new pressure sensor, or a new pump.

The ecoTEC boilers are renowned for reliability but when a pump fails (part no. 178983) we advice that our boiler engineers come and replace as this isn’t something that can’t be done as a DIY.

F75 Fault

A sensor blockage can cause a F75 fault which is caused either by the build-up of carbon deposits and debris in the filter system from the lack of boiler servicing or the system was not properly cleaned and treated when it was installed (cheap quotes tend to be the reason). The ecoTEC pressure sensor (Vaillant part no. 20059717) can become a problematic issue if you don’t choose to have your boiler serviced every year.

Pump failures on the Vaillant ecoTEC boilers (Vaillant part no. 178983) are again caused by the lack of maintenance. These pumps are called Grundfos which are much more reliable than the Wilo pumps which had a high failure rate.

Another common Vaillant fault is F28 and F29. These two fault codes are common in winter when the condensate pipe is frozen.

Vaillant Boiler Leaks – One of the most common faults

One of the most common Vaillant boiler faults is a leaking boiler. Leaks can be a nightmare because not only can they cause water serious damage to your home, it can also cause damage to the electrical components inside the boiler.

A boiler leak should be taken as an emergency, If you find a leak you should call a qualified heating engineer in Northampton.

No heating or hot water

No heatnig or hot water can mean that there is something wrong with your Vaillant boiler. Your boiler can stop providing you heating or hot water for a few reasons such as:

It’s always best to call a boiler engineer to come and visit to inspect the boiler and resolve the issue.

Vaillant ecoTEC Pro & ecoTEC Plus

Fault/Error Code Possible Cause
F00/F0 Heating Flow Temperature Sensor interruption or Heating Flow NTC Thermistor fault.
F01/F1 Return temperature sensor interruption NTC (Negative Temperature Coefficient) plug not plugged in or has come loose.
F10 Flow Negative Temperature Coefficient short circuit – NTC defective, short circuit in cable harness.
F11 Return Negative Temperature Coefficient short circuit – NTC defective, short circuit in cable harness.
F20 Safety switch-off – Temperature limiter Incorrect earth connection between cable harness and boiler. – Loose connection?
F22 Safety switch-off – Low water pressure, No water pressure, or water pressure is too low in the boiler. – Cable to the pump or water pressure sensor loose.
F23 Safety switch-off – Temperature difference. Pump blocked or insufficient pump output. Air in boiler. Temperature too great.
F24 Safety switch-off – Temperature difference. Pump blocked or poor pump performance. Air in boiler. Temperature is rising to fast.
F25 Safety switch-off – Temperature difference. Break in the plug connection for optional flue gas safety thermostat. Temperature too high.
F26 Fault – Gas valve without function or Gas valve stepper motor not connected. Plug on the PCB not plugged in correctly.
F27 Safety switch-off – Flame simulation – Moisture on the electronics. Flame monitor defective. Gas solenoid valve leaking.
F28 Start-up failureIgnition unsuccessful. Air in gas or gas flow pressure too low. Condensate pipe blocked. Fault on the gas valve or plug on PCB incorrectly plugged in.
F29 Operation failureRe-ignition unsuccessful. Gas supply stopped or faulty earthing of boiler. Condensate pipe blocked. Transformer has spark failure.
F32 Fan fault – Plug at fan not correctly plugged in or Fan blocked. Sensor defective. Plug on PCB not correctly plugged in.
F49 eBUS fault – Short circuit on eBUS. What is eBUS? – eBUS is a communication protocol used to manage your Vaillant boiler.
F61 Gas valve regulation – Short circuit/short to earth.
F62 Gas valve switch-off – Delayed shutdown of gas valve. Gas valve leaking or Electronics defective.
F63 EEPROM error – Electrically Erasable Programmable Read-Only Memory error. Electronics defective.
F64 Electronics or NTC fault
F65 Electronics overheating – Temperature fault. Electronics defective.
F67 Electronics or flame fault – Implausible flame signal or Electronics defective.
F68 Unstable flame – Air in gas, gas flow pressure too low, wrong air ratio.
F70 Invalid DSN – Invalid device specific number.
F71 Fault flow temperature sensor – Flow temperature sensor positioned incorrectly at supply pipe (CHECK) or Flow temperature sensor defective (New Sensor).
F72 Flow/return NTC fault – Negative Temperature Coefficient temperature difference too great or sensor defective. (New Sensor).
F73 Water pressure sensor – Sensor signal in the wrong range – too low. Short circuit of water pressure sensor or water pressure sensor defective. (New Sensor).
F74 Water pressure sensor – Sensor signal outside correct range – too high. Short-circuited at 5 V/24 or internal fault in water pressure sensor. Water pressure sensor defective. (New Sensor).
F75 Water pressure sensor – No pressure detection when starting pump. Water pressure sensor defective. (New Sensor). Check adjustable bypass.
F76 Overheating – Protection on primary heat exchanger has responded. Primary heat exchanger defective.
F77 No response from flue – Condensate pump fault or condensate pump defective.
F78 Interruption to DHW – Domestic hot water system outlet sensor at external controller UK link box is connected.
F83 Flow/return temperature sensor – Temperature change fault. When the burner starts, the temperature change registered non-existent or too small or not enough water in the boiler.
F84 Flow/return temperature sensor – Temperature difference implausible. Error with flow/return temperature sensor temperature changing error.
F85 Flow/return temperature sensor – Error with flow and return temperature, sensor incorrectly fitted . Fitted to the same pipe or wrong pipe.
F92 Coding resistor fault – he coding resistor on the PCB does not match. Check and enter the correct gas family.
F93 Gas group fault – Wrong gas restrictor or recirculation or wrong gas group. Internal pressure measuring point in venturi blocked. Do not use lubricant on O-ring.
S2, S22 Taps – Poor flow rate – The S2 and S22 fault code describes the rate at which water comes out of taps, shower heads and any other outlets. The poor flow rate means that the flow of water is slow.

Head Office:

THS Plumbing & Heating Northampton

3 Sunningdale Close



Tel: 01604 212732

Open: Monday-Sunday 7:30am - 10:00pm

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